A hard disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head that is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. Write heads make use of the electricity flowing through a coil; which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.
An HDD includes at least one head gimbal assembly (HGA) that generally includes a slider that houses the head, and a suspension. Each slider is attached to the free end of a suspension that in turn is cantilevered from the rigid arm of an actuator. Several semi-rigid arms may be combined to form a single movable unit, a head stack assembly (HSA), having either a linear bearing or a rotary pivotal bearing system. The suspension of a conventional disk drive typically includes a relatively stiff load beam with a mount plate at the base end, which subsequently attaches to the actuator arm, and whose free end mounts a flexure that carries the slider and its head.
The flexure in an integrated lead suspension is generally made out of a laminated multilayer material. Typically, it consists of a support layer (e.g., stainless steel “SST”), a dielectric insulating layer (e.g., polyimide), a conductor layer (e.g., copper), and a cover layer (e.g., polyimide) that insulates the conductor layer. The electrical lead lines are etched into the conductor layer, while the polyimide layer serves as the insulator from the underlying SST support layer. The SST support layer is also patterned to provide strength and gimbaling characteristics to the flexure. The conducting leads, called traces, electrically connect the head transducer to the read/write electronics. These traces are often routed on both sides of the suspension, especially in the gimbal region, and then along a suspension tail terminating at a connection with a flexible printed circuit (FPC) of a flexible cable assembly (FCA), with which the read/write electronics are coupled.
Typically, the suspension is fixed to the actuator arm by swaging and the suspension ground (GND) is connected with the actuator by way of this swaging. Because the swaging of the suspension is fixed at the arm actuator, there is a resonance node in the vicinity of the swaging. Furthermore, because the SST portion at the tip end of the suspension tail is not mechanically connected to anything, an electrical resonance mode exists in which the tail tip of the suspension constitutes the antinode of the resonance. For example, a quarter-wavelength resonance mode may be present with certain configurations. Because the suspension tail tip is not connected with GND, this is the electrical resonance mode of the SST portion of the suspension tail. This electrical resonance can introduce noise into the read path and/or may cause transmission line conversion from a common mode signal to a differential mode signal due to the unbalance.
The read inputs of the preamp need to receive a stable read signal that is minimally affected by interference, such as that which may be introduced by the electrical resonance mode associated with the suspension tail. Furthermore, as the number of conductors of the FCA increases, the GND pattern on the FCA has to be made narrower and, consequently, the impedance of the GND pattern increases. Therefore, the beneficial effect of grounding is diminished, even if the GND pad at the suspension tail tip is connected with the GND pad of the FCA. Consequently, a resonance mode is produced with an even longer electrical length, and the SER (symbol error rate) of the system is degraded by pickup of this resonance. Thus, reducing the electrical resonance is desirable.